1. Field of the Invention
The present invention related to a bicycle having a functional device operable by a force transmitted from a manual control device, and more particularly to a system for amplifying the above operating force for transmission to the functional device, e.g. a braking device or a change speed device.
2. Description of the Related Art
Conventionally, the functional device of a bicycle and the control device such as a control lever for operating the functional device are interconnected directly through a wire or the like. An operating force produced by the control lever is transmitted as it is to the functional device through the wire.
In the conventional construction, however, the operating force transmitted to the functional device depends solely on a force manually applied by the cyclist to the control lever. To apply a strong force to a braking device, for example, the cyclist must pull a brake lever hard against elasticity of a brake shoe or an urging force of a return spring included in the braking device. In operating a derailleur to change speed, a sufficient operating force must be applied to a change lever to overcome a resistance occurring with shifting of a chain from one gear to another and an urging force of a return spring included in the derailleur. Thus, a strong operating force must be applied manually to operate such a functional device, which is a considerable burden on the cyclist.
An improvement in the functional device per se has been proposed as a measure for solving this problem, in which the brake shoe is directly engageable with the rim of a wheel as in what is known as a leading cantilever brake. According to such a construction, an operating force relies only on positional relations between the brake shoe itself acting as a final active member of the functional device and the rim acting as a passive member. When, for some reason, the coefficient of friction between the brake shoe and rim exceeds a certain value, the brake shoe applies an increased braking force independently of an operating force controlled by the cyclist, or against the cyclist's will, and ultimately could lock the wheel.